Flexible circuits that feature multiple layers or levels of circuit traces formed on a flexible substrate are known. Reference is made, for example, to U.S. Patent Application Publication US 2008/0205010 (Haase). The flexible circuit is formed by building up on the flexible substrate, layer-by-layer, a series of electrically conducting, semiconducting and insulating layers and patterning each of them as necessary using conventional photolithographic techniques to provide the desired multilayered circuit design. The photolithographic techniques generally include applying a layer of photoresist atop the layer or layers to be patterned, patterning the photoresist layer using an ultraviolet (UV) light source in combination with a photomask, and removing exposed portions of the underlying layer or layers (i.e., those portions that lack any photoresist thereon) with a suitable etchant. The photolithographic techniques also include lift-off techniques that generally include applying a layer of photoresist atop a substrate, patterning the photoresist layer using an ultraviolet (UV) light source in combination with a photomask, depositing a layer or layers of circuit materials on the substrate and the patterned photoresist, and removing the remaining photoresist, thereby removing the portion of the layer or layers deposited on the photoresist. For circuits that have multiple layers or levels, a set of different photomasks is used, and fiducial marks are provided on each of the photomasks so that each photomask can be aligned with the pattern formed by a previous photomask in an attempt to ensure proper registration of the respective layers that form the circuit.
Existing roll-to-roll photolithography systems typically use a UV light source and glass or polymer photomasks to generate patterns in the photoresist. In some cases, the systems use a frame-by-frame step-and-repeat type procedure. See e.g. U.S. Pat. No. 5,198,857 (Goto). In other cases, the systems may use a continuous process. See e.g. US 2008/0011225 (McClure et al.).